It is often necessary to apply localized heat in a very precise manner to heat portions of articles during the manufacture thereof. For example, some containers are made from paperboard having a polymeric coating therein (i.e., so-called polycoated paperboard). During manufacture of containers from such polycoated paperboard, therefore, it is necessary for localized regions thereof to be heated rapidly and accurately in order to form high quality, leak-proof seams. Heating of the paperboard serves to soften the polymeric coating thereon to such an extent that when cooled the overlapped regions of the paperboard will be bonded one to another in a leak-proof manner.
Various techniques are known generally in the art for the purpose of localized heating of polycoated paperboard during the manufacture of containers therefrom. For example, according to one prior art technique, compressed air is heated either electrically or by means of a gas-fired heater. The heated air is then routed to the localized regions of the polycoated paperboard by means of suitable ducting. (See in this regard, U.S. Pat. No. 6,022,213, the entire content of which is incorporated hereinto expressly by reference.)
More recently, in U.S. Pat. No. 6,139,481 to Norwood et al (the entire content of which is incorporated hereinto expressly by reference), there is disclosed a gas-fired heater which serves to heat localized regions of polycoated paperboard directly. Direct localized heating of the polycoated board has a significant cost advantage over the indirect heating (e.g., using heated compressed air) techniques of the prior art. However, as larger containers are attempted to be manufactured, there exists a real nontrivial problem to ensure that the entire bottom wall seam is adequately heated and thus sealed sufficiently to prevent leakage.
It would therefore be highly desirable if gas-fired heaters could be provided for the direct localized heating of relatively large-sized polycoated paperboard containers during manufacture. It is therefore towards fulfilling such a need that the present invention is directed.
Broadly, the present invention is embodied in systems and methods for making a paperboard container wherein lateral side and the arcuate bottom edge regions of a paperboard sidewall blank may be heated simultaneously. In especially preferred embodiments, a sidewall blank heater assembly is provided having upper and lower sidewall blank heaters for simultaneously heating upper and lower edge strips of the sidewall blank adjacent lateral edges thereof, and a bottom sidewall seam heater for heating a generally curved strip adjacent an arcuate bottom edge of the sidewall blank simultaneously with the upper and lower edge strips. The sidewall blank is thereafter curved about a forming mandrel at a container-forming station so as to overlap the heated upper and lower edge strips of the sidewall blank to form a longitudinal container side seam, while the bottom edge of the sidewall blank is brought into contact with a paperboard bottom wall blank to form an annular container bottom seam. A bottom seam heater assembly is most preferably provided for circumferentially heating the container bottom seam simultaneously while the sidewall blank is curved about the forming mandrel at the container-forming station. In such a manner, high quality, leak proof seams of the paperboard container ensue.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.